Automatic traction control systems have been developed for automotive vehicles as a stability enhancement feature, and generally operate to reduce wheel torque in response to a detected wheel spin condition. A number of different approaches have been developed to affect control of a number of different variables in order to carry out the torque reduction, including the control of engine fueling, spark retard, and throttle, as well as various types of brake controls. In general, detection of the wheel spin condition is achieved by precisely monitoring the speeds of the driven wheels and comparing them with the speeds of un-driven wheels or a vehicle reference speed.
In conventional heavy-duty vehicles, traction control is commonly achieved using a form of engine torque output control. When a wheel-spin condition is detected, an automatic traction control (ATC) controller sends an engine torque reduction request via a data communication bus to an engine control module (ECM), such as a message sent via a Society of Automotive Engineers (SAE) J1939 controller area network (CAN) data link using the corresponding communication protocols. The SAE J1939 communication standards are commonly used in heavy-duty vehicles, and ATC controllers, engine controllers and data communication buses are commercially available that implement these standards. References herein to SAE J1939, and more specifically SAE J1939-71 “Vehicle Application Layer”, are based upon the Draft for Ballot dated Jun. 5, 1999.
Automatic traction controls for hybrid electric vehicles (HEV), such as heavy-duty trucks or buses, are not yet standardized and widely available, as such vehicles have limited commercial availability and widely varying powertrain systems and architectures. Various hybrid powertrain architectures are known for managing the input and output torques of various prime-movers in hybrid vehicles, most commonly internal combustion engines and electric machines. Series hybrid architectures are generally characterized by an internal combustion engine driving an electric generator which in turn provides electrical power to an electric drivetrain and to a battery pack. The internal combustion engine in a series hybrid is not directly mechanically coupled to the drivetrain. The electric generator may also operate in a motoring mode to provide a starting function to the internal combustion engine, and the electric drivetrain may recapture vehicle braking energy by also operating in a generator mode to recharge the battery pack. Parallel hybrid architectures are generally characterized by an internal combustion engine and an electric motor which both have a direct mechanical coupling to the drivetrain. The drivetrain conventionally includes a shifting transmission to provide the necessary gear ratios for a wide range of operation.
Electrically variable transmissions (EVT) are known which provide for continuously variable speed ratios by combining features from both series and parallel hybrid powertrain architectures. EVTs are operable with a direct mechanical path between an internal combustion engine and a final drive unit thus enabling high transmission efficiency and application of lower cost and less massive motor hardware. EVTs are also operable with engine operation mechanically independent from the final drive or in various mechanical/electrical split contributions thereby enabling high-torque continuously variable speed ratios, electrically dominated launches, regenerative braking, engine off idling, and multi-mode operation. Such powertrain systems are well adapted to control the output torque of the drivetrain, and thereby to implement automatic traction control. However, control methods and algorithms for implementing automatic traction control in hybrid electric vehicles, particularly those having EVT powertrain systems are needed.
Therefore, it is desirable to develop a method for providing automatic traction control in the powertrain systems of hybrid electric vehicles, particularly those having transmissions comprising an EVT. It is also particularly desirable to utilize existing communication standards, such as the SAE J1939 standard, as well as existing hardware and software that implement such standards, to implement a method for providing automatic traction control.